exponential day

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exponential day

Francis Boateng
Hi,
Please, how can I determine parameters from exponential equation
Example one:  y = a*exp(-b*x);  how do I determine �a� and �b�, as well as R-square from data sets. And also fitting y = a*exp(-b*x) into the data sets
Assuming data sets
A = (0,2,4,6,8,10)
B = (1,0.8,0.6,0.4,0.2,0.1)

Thanks
Francis


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Re: exponential day

S Ellison-2
> Please, how can I determine parameters from exponential equation Example
> one:  y = a*exp(-b*x);  how do I determine  a  and  b , as well as R-square
> from data sets. And also fitting y = a*exp(-b*x) into the data sets Assuming
> data sets A = (0,2,4,6,8,10) B = (1,0.8,0.6,0.4,0.2,0.1)

For least squares fitting, you could take logs and do a simple linear fit, if the resduals are reasonably homoscedastic in the log domain (or if you can sort the weighting out properly).

For non-linear least squares, look at ?nlm, ?nls or (if you want to roll your own) ?optim

For max likelihood, maybe nlme in the nlme package.

For other ideas, look up 'non-linear fitting with R' on any search engine, or check the R Task Views

S Ellison



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